Ken Pesyna , Kyle Wesson, Robert Heath Jr., Todd Humphreys
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Transcript of Ken Pesyna , Kyle Wesson, Robert Heath Jr., Todd Humphreys
Extending the Reach of GPS-assisted Femtocell Synchronization and Localization
through Tightly-Coupled Opportunistic Navigation
Ken Pesyna, Kyle Wesson, Robert Heath Jr., Todd Humphreys
Presentation at Globecom 2011 | December 5, 2011
Why Synchronization & Localization? Ensure reliable handover Reduce interference Operate within licensed
spectrum Locate emergency calls
Synchronization and Localization are key requirements for femtocells
Challenges of Satellite-based Synchronization Femtocells placed
indoors GPS signals weak: -155
dBW Up to 45 dB penetration
loss
Time and Frequency Requirements Minimum synchronization requirements
[Rakon]:
0 2 4 6 8 10 120
100
200
300
400
500
600
TD-SCDMA
WCDMA LTE
WiMAX
GSMCDMA2000
Requirements by Cellular Standard
Time Requirement (µs)
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These are very stringent requirements!
Spectrum licensing & operator control Emergency caller location identification
(E911)
Location Requirements
10m
20km
E911
Spectrum Licensing
Challenging!Big Issue: E911
0 2 4 6 8 10 120
100
200
300
400
500
600
TD-SCDMA
WCDMA LTE
WiMAX
GSMCDMA2000
Time Requirement (us)
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Prior Work Precision time protocol (PTP)
[Eidson02] Cellular network listen [Edwards08] GPS-based solutions
[Lewandowski99, Smith09]
20km
50 - 300m
5m
1-20 km
10m
Challenges of GPS
High signal sensitivity is required to acquire GPS signals indoors 5 dB-Hz to cover 90% of
residences
Sensitivity attainable today: State-of-the art via EGPS/AGPS
is 14 dB-Hz [RoDuJaGra08]
Goal: Close this 9 dB gap
Closing the 9 dB gap: Requirements Coherently integrate GPS signal over extended
interval1. Local oscillator drifts
This requires a more stable oscillator
2. # of time-frequency search cells explodes Increases probability of false alarm The search space must be reduced
Use ambient radio “signals of opportunity”: Stabilize femtocell’s local oscillator Narrow the GPS search space
Proposed Solution: Tightly-Coupled Opportunistic Navigation
Cellular HDTV
FinalAccumulation
Tightly-Coupled Opportunistic Navigation
Estimator
Benefits of Proposed TCON
1. Frequency stability transfer Correct its local clock variations to allow extended
integration
2. Search space contraint Aiding of precise time and frequency information Decreases time & frequency uncertainty
Ambient Signal Analysis
Analyzed ambient CDMA signals
Extremely stable and synchronous Signals remain stable beyond 9
seconds Time synchronized to 4 µs (2 of
3) Frequency accurate to 0.3 Hz
Mean-squared Coherence vs Time
9.5 s20 s
100+ s
Field Demonstration Cellular CDMA signals recorded in
Austin, TX TCON used to estimate the local clock
variations using only CDMA signals
Conclusions
Synchronization is required for femtocell operation
Location is required to meet FCC regulations
Existing approaches may not meet requirements
Propose TCON to exploit other available signals
Increases the GPS-sensitivity of the femtocell GPS meets the syncrhonization requirements Allows femtocells to be located further indoors
Conclusions
Requirements to acquire a 5 dB-Hz GPS signal: Coherent integration time of 7 seconds Time certainty to within 6 µs of GPS time Frequency certainty to within 0.5 Hz
TCON achieves the needed gain in sensitivity
Femtocells synchronized indoors using GPS
Questions?